The present invention relates to a valve timing regulation device which automatically varies the opening and closing timing of one or both of an intake valve and an exhaust valve in response to performance conditions of an internal combustion engine.
A conventional valve timing regulation device is already known which comprises a camshaft for opening and closing an intake valve and an exhaust valve of an internal combustion engine, a housing provided to rotate freely on the camshaft and driven to rotate by the output of the internal combustion engine, a rotor stored in the housing to be relatively rotatable and connected to the camshaft, and a lock means which operates with a mechanical urging force to restrict the relative, rotation of the housing and the rotor and which releases the restriction by the operation of a hydraulic control force (control hydraulic pressure) in a direction against the mechanical urging force.
FIG. 1 is a schematic cross sectional view showing the structure of a general internal combustion engine. In the figure, reference numeral 1 denotes a cylinder of an internal combustion engine, 2 is a piston which undergoes reciprocal motion in the cylinder 1, 3 is a crankshaft which is rotated by the reciprocal motion of the piston 2, 4 is a combustion chamber which combusts and explodes a gaseous mixture, 5 is an ignition plug which ignites the compressed gaseous mixture in the combustion chamber 4 with a spark, 6 is an air intake passage which supplies a gaseous mixture to the combustion chamber 4, 7 is an exhaust passage which exhausts the gases combusted in the combustion chamber 4, 8 is an intake valve which opens and closes the air intake passage 6, 9 is an exhaust valve which opens and closes the exhaust passage 7, 10a is a camshaft near the air intake. The air intake camshaft 10a has a cam 11a which drives the opening and closing of the intake valve 8, 11b is a camshaft near the exhaust and has a cam 11b which drives the opening and closing of the exhaust valve 9. 12a is a timing pulley or a timing sprocket near the air intake which is rotatably fitted and retained on the air-intake camshaft 10a. 12b is a timing pulley or a timing sprocket near the exhaust which is rotatably fitted and retained on the exhaust camshaft 11b. 13 is a timing chain or a timing belt which links the timing pulley or the timing sprocket 12a, 12b with the crankshaft 3.
A valve timing regulation device is provided in the air-intake camshaft 11a and the exhaust camshaft 11b of the internal combustion engine.
FIG. 2 is a cross sectional view in an axial direction of a first conventional valve timing regulation device as disclosed for example in JP-A-10-68306. The first conventional valve timing regulation device regulates the opening and-closing timing of the exhaust valve 9 in FIG. 1. In FIG. 2, those components which are the same as or similar to those shown in FIG. 1 are designated by the same reference numerals.
In FIG. 2, reference numeral 14 denotes a fixed camshaft sleeve securely fitted with a camshaft 10b near an exhaust (hereafter this will simply be referred to as camshaft). The timing pulley 12b near the exhaust is arranged rotatably on the camshaft 10b through the camshaft sleeve 14. Thus, the camshaft 10b and the camshaft sleeve 14 rotate together. The timing pulley 12b rotates relative to the camshaft 10b. 
12c is a projection for catching the spring thereon, which is integrally formed on one face of the timing pulley 12b and projects therefrom. 15 is a spiral spring, an outer radial side end portion of which is hung on the projection 12c and an inner radial side end portion of which is hung on the camshaft sleeve 14. The spiral spring 15 urges the rotor 18 (discussed hereafter) in an advancing direction, the urging force is set to be greater than the maximum torque when the internal combustion engine is started.
16 is a housing which is fixed by a bolt 17 on the timing rotation body 12b, 16a is an annular partition which is formed in the middle of an inner peripheral surface of the housing 16. An internal section of the housing 16 is partitioned by the partition 16a into a rotor storage chamber 16b on one axial end and a spring storage chamber 16c on the other axial end. The spiral spring 15 is stored in the spring storage chamber 16c. 
18 is a rotor which is rotatably stored in the rotor storage chamber 16b of the housing 16. The rotor 18 is fixed with an axial bolt 19 to an end portion of the camshaft 10b and is adapted to rotate together with the camshaft 10b. Thus, the housing 16 and the rotor 18 can rotate relative to one another.
20 is a covering member which covers the open end of the housing 16 and is fixed with a bolt 21to the housing 16.
FIG. 3 is a cross sectional view of the first conventional valve timing regulation device along the line Axe2x80x94A in FIG. 2. In the figure, reference numeral 22 denotes a plurality of shoes which project from an inner peripheral surface of the housing 16. The shoes 22 are integrated with the housing 16, the tips of the shoes 22 are in slide contact with the rotation body of the rotor 18. Reference numeral 23 denotes a plurality of vanes which project from an outer peripheral surface of the rotor 18 and extend in a radial direction. These vanes are integrated with the rotor 18, the tips of the vanes 23 are respectively in slide contact with the inner peripheral surface of the housing 16 between the shoes 22. An advance hydraulic chamber 24 and a retard hydraulic chamber 25 each having a fan-shaped space is formed between the shoes 22 and the vanes 23. A hydraulic oil is supplied from the hydraulic control system (not shown) to the advance hydraulic chamber 24 and the retard hydraulic chamber 25 in accordance with the operation condition of the internal combustion engine.
As described above, the first conventional valve timing regulation device is provided with a lock mechanism (not shown) for locking the rotor 18 at a maximum advance position with respect to the housing 16. The lock mechanism includes a stopper which is contained in the rotor 18 to be displaceable in its axial direction and a stopper hole which is formed on a cover member to engage and disengage with the stopper. The lock mechanism is also provided with a valve timing regulation mechanism on the air intake side which regulates the opening and closing timing of the intake valve 8 in FIG. 1. The lock mechanism of the intake side valve timing regulation device is adapted to lock the rotor at a maximum retard position in an opposite manner to that of the exhaust side valve timing regulation device.
Next, the operation of the first conventional valve timing regulation device will be described below.
Firstly, in FIG. 1, a rotational force of the crankshaft 3 is transmitted respectively to the intake side camshaft 11a and the exhaust side camshaft 11b through the timing pulleys 12a, 12b by the timing belt 13 during operation of the internal combustion engine. At this time, the rotor 18 and the housing 16 as shown in FIG. 2 and FIG. 3 are in a lock released state. The opening and closing timing of the intake valve 8 and the exhaust valve 9 in FIG. 1 is regulated by the relative rotation of the housing 16 and the rotor 18 due to a pressure differential of the advance side hydraulic chamber 24 and the retard side hydraulic chamber 25 to which a hydraulic oil is supplied from the hydraulic control system in accordance with the operation condition of the internal combustion engine.
When the internal combustion engine is stopped after operating, a rotational reaction force in the retarding direction is generated respectively to the intake side camshaft ha and the exhaust side camshaft 11b shown in FIG. 1. The lock position of the air-intake side camshaft 11a is set to a maximum retarded position and the lock position of the exhaust side camshaft 11b is set to a maximum advanced position. Therefore, when the internal combustion engine is stopped, although the intake side camshaft 11a is locked in the maximum retarded position, the exhaust side camshaft 11b tends to rotate in the retarding direction which is the opposite direction to the locked position. In this case, the exhaust side camshaft 11b is urged in the advancing direction by the spiral spring 15 through the rotor 18 which rotates together with the exhaust side camshaft 11b. Therefore, the exhaust side camshaft 11b is not affected by the rotational reaction force when the internal combustion engine is stopped, the rotor 18 is locked in the housing 16 by the locking mechanism at the maximum advanced position. In such a way, the housing 16 and the rotor 18 can rotate together when the internal combustion engine is started.
Since the first conventional valve timing regulation device is constructed above, in order to allow assembly of the spiral spring 15, it is necessary to integrate the projection 12c on the stem of the timing pulley 12b and to form the camshaft sleeve 14 as a separate component from the camshaft 10b. Furthermore, it is necessary to form a spring storage chamber 16c separated from the rotor storage chamber 16b by the partition 16a in the housing 16 in order to maintain an assembly space for the spiral spring 15. Therefore, problems related to structural complexity and increases in costs have arisen. In particular, when assembling the spiral spring 15, one end is attached to the projection 12c and the other end is attached to the camshaft sleeve 14 while the spiral spring 15 is twisted. Thus, assembly of the spiral spring 15 is complicated to an extreme degree by the generation of a torsional reactive force in the spiral spring 15 during attachment. Moreover, by the reactive torsion force of the spiral spring 15, the spiral spring 15 itself becomes entangled, and further, the vanes 23 of the rotor 18 become inclined or undergo a positional deviation in the radial direction. This increases a sliding resistance between the rotor 18 and the housing 16. Such problems have arisen with respect to assembly accuracy land assembly operations for the spiral spring 15. Furthermore, the problem has also arisen of increases in rotation resistance of the camshaft 10b by the sliding contact of the spiral spring 15 after assembly with the lateral face of the timing pulley 12b or the partition 16a of the housing 16.
FIG. 4 is a cross sectional view along an axial direction showing the structure of a second conventional valve timing regulation device as disclosed for example in JP-A-10-68306. FIG. 5 is a cross sectional view of the second conventional valve timing regulation device along the line Bxe2x80x94B in FIG. 4. Those components which are the same as or similar to those in FIG. 1 to FIG. 3 are denoted by the same reference numerals and additional description will be omitted. In the figure, reference numeral 26 denotes a rear plate having a boss portion which is rotatably fitted on an outer periphery of a camshaft sleeve 14. The rear plate 26 is fixed integrally with the timing pulley 12b, the housing 16 and the cover member 20 by a bolt 17a. 26a is a projection for catching the spring thereon, which projects from a lateral face of the flange of the rear plate 26. The projection 26a is integrated with the flange of the rear plate 26. 27 is a torsion spring which urges the camshaft 10b in its advancing direction, the torsion spring 27 is inserted into a ring-shaped space formed between an outer peripheral surface of the camshaft sleeve 14 and an inner peripheral surface of the boss portion of the rear plate 26. One end of the torsion spring 27 is attached to the camshaft sleeve 14 and the other end is attached to the projection 26a. Since the operation of this second conventional example is the same as that of the first conventional example, further description will be omitted.
Since the second conventional valve timing regulation device is constructed as above, it is necessary to form the rear plate 26 separately as an assembly component for the torsion spring 27. As a result, the number of components and the number of component assembly steps are increased, thereby to increase the cost. Furthermore, assembly of the torsion spring 27 is extremely complicated. In particular, since the assembled torsion spring 27 is in slide contact with the outer peripheral surface of the camshaft sleeve 14 and the inner peripheral surface of the boss portion of the rear plate 26, the problem has arisen that the sliding resistance of the torsion spring 27 is increased, thereby to affect the opening and closing timing of the valve.
FIG. 6 is a cross sectional view along an axial direction of a third conventional valve timing regulation device as disclosed for example in JP-A-10-68306. Those components which are the same as or similar to those in FIG. 1 to FIG. 5 are denoted by the same reference numerals and additional description will be omitted. In the figure, reference numeral 22a denotes a shoe side concavity which is provided on a peripheral end face towards an advancing direction in each shoe 22 of the housing 16. 23a is a vane side concavity which is provided on a peripheral end face towards a retarding direction in each vane 23 of the rotor 18. 28 is a coil spring both ends of which are directly fitted into the shoe side concavity 22a and the vane side concavity 23a. The spring 28 urges the rotor 18 in the advancing direction with respect to the housing 16. Thus, in the third conventional example as well, the rotor 18 is displaced in a rotational direction to a maximum advanced position by the urging force of the spring 28 when the internal combustion engine is stopped, and the rotor 18 is locked with respect to the housing 16 at the maximum advanced position.
Since the third conventional valve timing regulation device is constructed as above, it is necessary to fit both ends of the spring 28 directly into the shoe side concavity 22a and the vane side concavity 23a in the advancing hydraulic chamber 24 from a peripheral direction while compressing the spring 28. Thus, the problem has arisen that there is a high probability of reductions in assembly productivity of the spring 28 due to the generation of a curvature or a compressive reaction force of the spring 28 when fitting the spring. In particular, since, as stated above, both ends of the spring 28 are directly fitted to the shoe side concavity 22a and the vane side concavity 23b, there is a high probability of wear being caused in the fitting portion of the spring 28 by the friction between the spring 28 and the inner walls of the shoe side concavity 22a and the vane side concavity 23b. Furthermore, the problem has arisen that there is a high probability of generating a positional deviation of the spring, thereby causing detachment of the spring 28 from the shoe side concavity 22a and/or the vane side concavity 23b or causing the wear in contact with the covering components in the axial direction which constitute the hydraulic chamber.
The present invention is proposed to solve the above problems and has the object of providing a valve timing regulation device which can improve assembly productivity of the rotor urging member for urging the rotor in a direction opposite to the rotational reactive force generated on the camshaft when the internal combustion engine is stopped, and which can prevent wear of the rotor urging members.
Further, it is an object of the present invention to provide a valve timing regulation device which allows simple and well-balanced assembly of the rotor urging member so that the rotor in the housing does not undergo a positional deviation in an axial or radial direction, thereby to improve both of the assembly productivity and the assembly accuracy and to simplify the component structure.
Furthermore, it is an object of the present invention to provide a valve timing regulation device which can ensure retention of the holder members, which support both ends of the rotor urging member, on the vane of the rotor and the shoe of the housing.
Furthermore, it is an object of the present invention to provide a valve timing regulation device which allows simple formation of the holder members.
Furthermore, it is an object of the present invention to provide a valve timing regulation device which enables the rotor urging member to display a buffering function by the holder members.
Further, the present invention has the object of providing a valve timing regulation device which allows mass production of the holder member having sufficient mechanical strength, and allows cost reductions and improvements in productivity.
Furthermore, the present invention has the object of providing a valve timing regulation device which allows simple assembly of a plurality of rotor urging members, which is united with the holder member, into the same hydraulic chamber, and which allows further, improvements to assembly accuracy without entanglement of the plurality of rotor urging members.
Furthermore, the present invention has the object of providing a valve timing regulation device, which ensures sufficient mechanical strength of the shoes and the vanes to which the rotor urging member is attached.
Furthermore, the present invention has the object of providing a valve timing regulation device, which allows further simplification in the assembly of the holder members united with the rotor urging member.
Furthermore, the present invention has the object of providing a valve timing regulation device, which allows downsizing the device by disposition of the rotor urging member in the advancing hydraulic chamber.
Furthermore, the present invention has the object of providing a valve timing regulation device which allows simple attachment of the holder members, which are formed as a unit together with the rotor urging member, to the vanes and the shoes, and allows improvement of the reliability of the device by preventing the holder members from detaching from the shoes and the vanes.
According to the present invention, there is provided a valve timing regulation device including: a camshaft which drives the opening and closing of valves in an internal combustion engine; a housing which has a plurality of shoes on an inner peripheral face, the housing being arranged to rotate freely on the camshaft and rotated with the output of the internal combustion engine; a rotor having a plurality of vanes which define a retarding hydraulic chamber and an advancing hydraulic chamber in cooperation with the wall surfaces of the shoes directed to a circumferential direction, the rotor being stored in the housing to rotate relative to thes housing and coupled to the camshaft; and a lock means which is operated by a mechanical urging force and restricts the relative rotation of the rotor and the housing, the lock means releasing the restriction by operation of a hydraulic pressure in a direction against the mechanical urging force, the valve timing regulation device further comprising: a rotor urging member disposed between the wall surfaces of the shoes and vanes directed to the circumferential direction for urging the rotor in a rotational direction towards a predetermined lock position with respect to the housing; and a pair of holder members mounted on the wall surfaces of the shoes and vanes for supporting both ends of the rotor urging member.
In such a valve timing regulation device, since the ends of the rotor urging member are supported on-the wall surfaces of the shoe of the housing and the wall surfaces of the vane of the rotor through the holder members, it is possible to prevent wear of the rotor urging member due to friction with the walls of the shoes and vanes. Further, since a unit of the rotor urging member and the holder members is attached utilizing the hydraulic chambers which is formed between the shoes and the vanes, it is not required to provide a separate space to allow attachment of this unit, and thus, it is possible to downsize the valve timing regulation device and simplify its structure.
The valve timing regulation device of the present invention may be adapted so that an even number groups of advancing hydraulic chambers and retarding hydraulic chambers are formed between the wall surfaces of the vanes and the shoes, the rotor urging member is arranged in a pair of the advancing hydraulic chambers situated in an axial symmetry position of the rotor, and both ends of the rotor urging member are supported by the pair of holder members mounted on the wall surfaces of the vane and shoe which are disposed on both sides of the advancing hydraulic chamber to sandwich the rotor urging member.
In such a valve timing regulation device, since a unit of the rotor urging member and the holder members disposed on both ends thereof is attached only in the advancing hydraulic chambers arranged in an axial symmetry position of the rotor, it is possible to reduce the number of the holder members and the rotor urging members to be used, and to improve balance of the urging force on the rotor. As a result, it is possible to suppress entanglement and inclination of the rotor.
In the valve timing regulation device of the present invention, a holder engagement portion for fitting the holder member may be formed on the wall surfaces of the vane and the shoe directed toward the circumferential direction.
In such a valve timing regulation device, the valve timing regulation device allows simple assembly of the rotor urging member by merely fitting the holder members, which is united with the rotor urging member, into the holder engagement portions of the vane and the shoe. This allows improvements in assembly productivity and also ensures support of the holder members disposed on both end portions of the rotor urging member.
In the valve timing regulation device of the present invention, the holder members may be integrally formed with a resin material to have an engagement projection or an engagement hole which is fitted with the end portion of the rotor urging member.
In such a valve timing regulation device, since the holder member is formed from an integrated resin component, it is possible to improve the productivity and reduce the cost. Furthermore, the holder members and the rotor urging member can be easily assembled as a unit by merely fitting both ends of the rotor urging member with the engagement hole or the engagement projection of the holder members.
In the valve timing regulation device of the present invention, the holder member may be integrally formed with a resilient member such as hard rubber and have an engagement hole or an engagement projection enabling fitting of both ends of the rotor urging member.
In such a valve timing regulation device, since the holder member is formed with an integrated component of the resilient member such as hard rubber, it is possible to improve the productivity and reduce the cost. Further, the holder members and the rotor urging member can be easily assembled as a unit by merely fitting both ends of the rotor urging member into the engagement hole or the engagement projection of the holder members. Furthermore, it is possible to display a buffer function of the rotor urging member sufficiently by the provision of the holder members.
In the valve timing regulation device of the present invention, the holder members may be formed with a pressed sheet metal member.
In such a valve timing regulation device, it is possible to effect mass production of the holder members by a pressing process of the metal plate. Furthermore, it is possible to ensure a sufficient mechanical strength for the holder members.
In the valve timing regulation device of the present invention, the holder members, which have an engagement hole or an engagement projection to fit with the end portions of the rotor urging member, may be integrally formed by a molding process such as casting or forging of a metallic material.
In such a valve timing regulation device, since the holder member is formed as a metallic molded component by a process such as forging or casting of the metallic material, it is possible to improve the productivity and reduce the cost. Furthermore, it is possible to easily assemble the rotor urging member and the holder members as a unit by merely fitting both ends of the rotor urging member into the engagement hole or the engagement projection of the holder members.
In the valve timing regulation device of the present invention, the rotor urging member may be at least two coil springs, both ends of which are supported by a pair of holder members and which are stored in the same advancing hydraulic chamber, the coil springs having coil wire diameter different from each other.
In such a valve timing regulation device, the coil springs, which are arranged in parallel and supported at both ends by a pair of holder members, have different size in diameter of coil wire from; each other, and thus the coil springs are also different in coil pitch (wire-to-wire distance) from each other. Thus, even in the unlikely event that the parallel springs, which are assembled as a unit together with the holder members, undergo a bending compression, the springs do not become entangled. Therefore, it is possible to further improve assembly accuracy by suppression of meshing or inclination of the rotor as a result of such entangling.
In the valve timing regulation device of the present invention, the rotor urging member which is supported at both ends by a pair of holder members and is stored in the same advancing hydraulic chamber may be constituted by at least two coil springs with different number of turns.
In such a valve timing regulation device, since the coil springs, which are arranged in parallel and supported at both ends by a pair of holder members, are formed with the different number of turns, the coil pitch (wire-to-wire distance) in respective coil springs is also different. Thus, even in the unlikely event that the parallel springs, which are assembled as a unit together with the holder members, undergo a bending compression, the springs do not become entangled. Therefore, it is possible to further improve the assembly accuracy by suppression of meshing or inclination of the rotor as a result of such entangling.
According to the present invention, the valve timing regulation device may be adapted so that the peripheral lengths of the shoes and vanes to be disposed on both sides of the advancing hydraulic chambers which store the rotor urging member, is longer than those of the shoes and vanes to be disposed on both sides of the other advancing hydraulic chambers which do not store the rotor urging member.
In such a valve timing regulation device, since the peripheral lengths of the shoes and the vanes to be disposed on both sides of the advancing hydraulic chambers which stores the rotor urging member is longer than those of the shoes and the vanes to be disposed on both sides of the other advancing hydraulic chambers which do not store the rotor urging member, it is possible to ensure a sufficient mechanical strength for the shoes and the vanes on which the holder members supporting both ends of the rotor urging member are attached.
According to the present invention, the holder engagement portion may be formed as axial grooves, which allow insertion of the holder members from one axial end.
In such a valve timing regulation device, when mounting the unit of the rotor urging member and the holder members, it is possible to attach the unit of the rotor urging member and the holder members efficiently and easily by merely inserting the holder members from one axial end into the axial grooves formed on the wall surfaces of the shoe and the vane oriented to the circumferential direction. Thus, assembly productivity is further improved. Further, as described above, since the holder members are attached by direct insertion into the axial grooves of the shoe and the vane, a separate component for assembly is not necessary. Thus, the structure can be simplified and cost reductions can be realized. Furthermore, the valve timing regulation device can be downsized.
According to the present invention, the holder engagement portion may be formed as holes which are opened in the wall surfaces of the shoe and the vane.
In such a valve timing regulation device, when mounting the unit of the rotor urging member and the holder members, it is possible to attach the unit of the rotor urging member and the holder members efficiently and easily by fittingly inserting the holder members into the holes opened on the wall surfaces of the shoe and the vane oriented to the circumferential direction. Thus, assembly productivity is further improved. Further, since a separate component is not required for mounting the holder members as this is in the form of the holes provided on the wall surfaces of the shoe and vane, the structure can be simplified by the reduction in component number and cost reductions can be realized. Furthermore, the valve timing regulation device can be downsized.
According to the present invention, the valve timing regulation device may be adapted so that the holder engagement portion is formed as axial grooves which allow insertion of the holder members from one axial end, and a holder detachment prevention means is provided on at least one of the axial grooves and the holder members, the holder detachment prevention means limiting the displacement of the holder members in the axial grooves with respect to a rotation direction of the device.
In such a valve timing regulation device, even if vibration or an unlikely unforeseen event occurs, detachment of the holder members in the rotation direction of the device is not possible and accurate operation of the device can be ensured.
In the valve timing regulation device of the present invention, the holder detachment prevention means may bed formed by a tapering face provided on a lateral wall surface of the holder engagement groove to gradually narrow the groove width of the holder engagement groove towards an opened end of the groove, and an another tapering face provided on a lateral wall surface of the holder member in alignment with the tapering face.
In such a valve timing regulation device, the holder detachment prevention means can be provided easily by merely forming the lateral wall surfaces of the holder members and the holder engagement grooves in a tapering shape. Thus, even if vibration or an unlikely unforeseen event occurs, detachment of the holder members in the rotation direction of the device is not possible and accurate operation of the device can be ensured.
In the valve timing regulation device of the present invention, the holder detachment prevention means may be formed as a catch for preventing detachment which engages with the holder member disposed in the holder engagement groove, the catch being arranged in an opened end of the respective holder engagement grooves of the shoe and the vane.
In such a valve timing regulation device, the holder detachment prevention means can be provided easily by merely forming the catch in the opened end of the respective holder engagement grooves of the shoe and the vane. Thus, even if vibration or an unlikely unforeseen event occurs, detachment of the holder members in the rotation direction of the device is not possible and accurate operation of the device can be ensured.
In the valve timing regulation device of the present invention, the holder detachment prevention means may be formed by engagement concavities arranged on one of the holder, members and the holder engagement grooves of the shoe and the vane, and engagement protrusions arranged on the other of the holder members and the holder engagement grooves, the engagement concavity and the engagement protrusion being engaged with each other.
In such a valve timing regulation device, the holder detachment prevention means can be provided easily by merely forming the engagement concavities on one of the holder members and the holder engagement grooves and the engagement protrusions on the other of the holder members and the holder engagement grooves. Thus, even if vibration or an unlikely unexpected event occurs, detachment of the holder members in the rotation direction of the device is not possible and accurate operation of the device can be ensured.
In the valve timing regulation device of the present invention, the holder detachment prevention means may be formed by key grooves formed on both of the holder members and the holder engagement grooves of the shoe and vane, and a key member inserted into both key grooves.
In such a valve timing regulation device, it is possible to fix the holder members in the holder engagement grooves by merely inserting the key member into both key grooves of the holder member and the holder engagement groove. Thus, even if vibration or an unlikely unexpected event occurs, detachment of the holder members in the rotation direction of the device is not possible and accurate operation of the device can be ensured.